1. Field Of The Invention
This invention relates to stapling machines, hereinafter called staplers, and more particularly to improvements of a staple cartridge for a stapler in which a number of staple sheets are stacked and delivered by a conveying belt to the forming and driving section thereof. Such staple blanks sheets are formed by bonding a plurality of straight wire staples blanks together in the form of a sheet.
2. Description Of Related Art
In the prior art staples are successfully supplied with a pawl to the forming and driving section. In such a stapler the staples are formed into a roll using a piece of tape as well as an adhesive. This double adhesive is necessary in order to reliably hold the staples together into the roll. The roll is then loaded into a cartridge and thus is fed into the stapler. The disadvantages of this system are twofold. First, the taping involves an extra step in the manufacturing of the staple roll. In addition, the tape tends to separate from the roll when the driving means drives a formed staple placed in a driving position and interfere with the driving mechanism, so that the staple hammaring operation may not be achieved.
U.S. Pat. No. 4,623,082 to Kurosawa discloses a stapler cartridge which feeds staples in sheets, rather than rolls, eliminating the need for tape in securing the staples together. While the Kurosawa invention has eliminated the problems associated with the use of tape in staple cartridges it is susceptible to periodic jamming of staple sheets in the staple sheet let-off opening. In addition, because of the large frictional forces on the guide member in the Kurosawa invention the staple sheet conveyor belt 7 does not convey the staple sheet with great reliability.
In order to illustrate the novelty and utility of the present invention the operation of the Kurosawa invention will be discussed in greater detail. Referring to FIG. 1(a) and FIG. 1(b) prior art, in order to feed a staple sheet S' from the cartridge A' to the forming and driving section of the stapler, the lowermost staple sheet Sa in the staple sheet accommodating section 1' is moved out through the staple sheet let-off opening 3' by means of a conveyor belt 7' . The staple sheet is held between the upper surface 7a' the conveyor belt 7a' of the conveyor belt 7' and the lower surface 13b' of a guide member 13', the frictional force between the conveyor belt and the staple sheet being utilized to transport the staple sheet. In order to prevent excessive frictional force between the guide member and the staple sheet the area of contact between the two is minimized. This is accomplished by providing a recess portion 13c' in the lower surface of the guide member so that only the edges of the staple sheet are in contact with the guide member 13'. The width of the conveyor belt is much smaller than that of the staple sheet and therefore the edges of the staple sheet are pushed downwards by the guide member and the middle of the staple sheet is pushed upwards by the conveyor belt. This imparts a curvature in the staple sheet as seen in FIG. 1(b). As a result, the area of contact between the conveyor belt and the staple sheet is minimized, as is the frictional force, causing the undesirable effect of inconsistent conveying of the staple sheet to the forming and driving section of the stapler.
Kurosawa provides for a magnetic means (not shown) placed directly below the conveyor belt 7' in order to alleviate the problem of insufficient contact between the conveyor belt 7' and the staple sheet S'. In order to cause a magnetic field of sufficient force the magnetic means must be as close to the conveyor belt 7' as possible, preferably in contact with it. Because the conveyor belt 7' is moving the resultant frictional force at the interface with the magnetic means causes premature wear of the conveyor belt 7'. Also, the magnetic means is limited in length in order to be disposed between the two pulleys of the conveyor belt 7'. Thus the magnetic means is not effective over the whole travel of the staple sheet S'. In summary, the magnetic means is undesirable because it is not entirely effective and it creates added expense in the manufacture, and maintenance in the operation, of the staple machine.
Referring now to FIG. 2(a) and FIG. 2(b) prior art, it is shown that the inside dimensions of the accommodating section 1' is larger than the staple sheets S' thereby creating a clearance C' between the inner wall of the cartridge and the stack of staple sheets. The cartridge is mounted so as to be inclined toward the rear wall 9' of the cartridge therefore allowing the vibration of the stapler to keep the staple sheets in contact with the rear wall. Under this condition, the lowermost staple sheet Sa' is conveyed by the conveyor. As the staple sheet Sa' is being conveyed through the let-off opening 3' the second staple sheet Sb' begins to contact the conveyor belt 7' and is pushed up against a sloped surface 3a' just above the let-off opening preventing the second staple from entering the let-off opening. As a result, the weight of the remaining staples in the stack acts as a shearing force on the front of the second staple sheet which is not in contact with the conveyor belt. This shearing force tends to bend the staple sheet Sb', as shown in FIG. 2(b), resulting in periodic jamming of the staple sheet in the let-off opening.